Ultraviolet curable silver composition and related method

ABSTRACT

A photocurable silver composition is provided which comprises an ultraviolet light curable organic mixture, a photoinitiator, a silver powder, and a silver flake composition. The silver flake composition comprises at least 20% of the weight of the silver powder. The disclosed compositions may be used to produce silver-containing coatings on a variety of different substrates. Related methods are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 09/413,577 filed on Oct. 6, 1999 which is acontinuation-in-part of U.S. application Ser. No. 09/291,774, filed Apr.14, 1999.

TECHNICAL FIELD

[0002] The present invention relates to silver-containing compositionsand more particularly to photocurable silver-containing compositions, tomethods for making and applying a photocurable silver-containingcompositions as a coating on a substrate.

BACKGROUND ART

[0003] There are many instances in which it is necessary or desirable toapply a coating, plating or layer of silver or a silver-containingcompound to a substrate. Examples of such applications would includeelectrode plating for switches such as those used on pressure-sensitiveswitches or control panels, for example, as are used on appliances suchas microwave ovens, conventional ovens, and the like. Such silverplating also is commonly used in the semiconductor fabrication arts toapply silver metalizations on silicon or germanium semiconductor wafers.Other examples of such substrates include, without limitation, suchthings as polyesters, polycarbonates, vinyls, ceramics, glass, and thelike.

[0004] The predominant approach heretofore used in applying silver tosubstrates has involved using a solvent-based silver solution to thesubstrate, and chemically or thermally curing the solution to evaporatethe solvent. This leaves the solid silver plating on the substrate.

[0005] This conventional approach is disadvantageous in a number ofrespects. Of perhaps the greatest concern is the fact that the solventscurrently used for this purpose are toxic. They require special handlingand disposal facilities and techniques, and correspondingly increaseinefficiencies and costs. Even while observing these special handlingtechniques, they present hazards to workers using these toxic materials.The solvent-based compositions and methods also are disadvantageous inthat it can be difficult to predict the uniformity and thickness of theresultant silver plating after the solvent has evaporated. This leads toquality and performance variations.

SUMMARY OF THE INVENTION

[0006] Accordingly, an object of the present invention is to provide asilver composition and method in which silver can be disposed on asubstrate without requiring a toxic solvent.

[0007] Another object of the invention is to provide a silvercomposition and method in which disposition of the silver layer can bedone more quickly and efficiently than prior art solvent-basedtechniques.

[0008] Another object of the invention is to provide a silvercomposition and method in which a silver coating may be created whichhas more predictable and uniform layer thickness relative to prior artsolvent-based systems.

[0009] To achieve the foregoing objects, and in accordance with thepurposes of the invention as embodied and broadly described in thisdocument, a silver composition is provided for deposition as a coating,plating, film or layer on a substrate. The terms coating, plating, filmand layer in the context of this document are used to refer generally toa covering on the surface of a substrate, which covering may be of avariety of thicknesses depending on the application and the designgoals.

DISCLOSURE OF INVENTION

[0010] In accordance with one aspect of the invention, a photocurablesilver composition is provided. The silver composition comprises aphotocurable organic mixture, a photoinitiator, a silver powder, and asilver flake composition. The silver flake composition is present in anamount of at least 20% of the weight of the silver powder present in thecomposition. Incorporation of silver flake composition in an amount ofat least 20% results in films with superior conductivity. Resistivitiesas low as 0.03 ohm/sq at 1 mil are achieved.

[0011] The photocurable silver composition preferably comprises analiphatic acrylated oligomer, wherein the aliphatic acrylated oligomeris present in an amount of about 3% to 8% based on the weight of thesilver composition. All percentages of the silver composition asexpressed in this document, unless otherwise stated, refer to the masspercentage of the stated component to the total mass of the silvercomposition in its fluid uncured state at standard temperature andpressure.

[0012] The silver composition also preferably comprises an acrylatedepoxy oligomer, wherein the acrylated epoxy oligomer is present in anamount of about 2% to 4% of the silver composition.

[0013] The silver composition also preferably comprises an isobomylacrylate monomer in an amount of about 4% to 8% of the silvercomposition, a photoinitiator in an amount of about 3% to 6% of thesilver composition, a flow promoting agent in an amount of about 0.1% to2% of the silver composition, a silver powder in an amount of about 50%to 60% of the silver composition, and a silver flake composition in anamount of about 25% to 35% of the silver composition.

[0014] In accordance with this aspect of the invention, the aliphaticacrylated oligomer preferably comprises a urethane oligomer. Inpresently preferred versions of the silver composition, the aliphaticacrylated oligomer is present in an amount of about 8% of the silvercomposition.

[0015] The acrylated epoxy oligomer is preferably present in an amountof about 3% of the silver composition. The isobornyl acrylate monomer ispreferably present in an amount of about 5% of the silver composition.The photoinitiator is preferably present in an amount of about 5% of thesilver composition. The flow promoting agent is preferably present in anamount of about 1% of the silver composition.

[0016] In presently preferred embodiments according to this aspect ofthe invention, the silver powder preferably but optionally is present inan amount of about 52% of the silver composition. In these preferredembodiments, the silver powder has a particle size range of about 5microns to about 15 microns. In a more preferred embodiment, the silverpowder has a particle distribution such that about 5% to 20% of theparticles have a particle size of less than about 4.7 microns, about 30%to 60% of the particles have a particle size of less than about 7.6microns, and about 70% to 95% of the particles have a particle size ofless than about 14.9 microns. In the most preferred embodiment, thesilver powder has a particle distribution such that about 10% of theparticles have a particle size of less than about 4.7 microns, about 50%of the particles have a particle size of less than about 7.6 microns,and about 90% of the particles have a particle size of less than about14.9 microns.

[0017] According to the presently preferred embodiments, the silverflake is present in an amount of about 30% of the silver composition.Preferably the silver flake has a particle size range of about 5 micronsto about 32 microns. The silver flake preferably has a flakedistribution such that about 10% of the particles have a particle sizeof less than about 5.5 microns, about 50% of the particles have aparticle size of less than about 12.5 microns, and about 90% of theparticles have a particle size of less than about 32.0 microns.

[0018] In a further refinement of the presently preferred embodiment, anadhesion promoter is present in about 1 to 4% of the silver composition.This further refinement improves adhesion to substrates coated withtransparent conductors such as indium tin oxide (ITO).

[0019] In accordance with another aspect of the invention, aphotocurable silver composition suitable for producing a coating that iscapable of shielding electromagnetic radiation is provided. Thisembodiment is preferably applied to a substrate by spraying. The silvercomposition comprises an acrylated epoxy oligomer, wherein the acrylatedepoxy oligomer is present in an amount of about 2% to 8% of the silvercomposition. The silver composition preferably comprises an isobornylacrylate monomer in an amount of about 15% to 30% of the silvercomposition, an photoinitiator in an amount of about 3% to 7% of thesilver composition, a flow promoting agent in an amount of about 0. 1%to 2% of the silver composition, a silver powder in an amount of about20% to 40% of the silver composition, and a silver flake composition inan amount of about 20% to 40% of the silver composition.

[0020] In accordance with another aspect of the invention, aphotocurable silver composition suitable for producing a coating that iscapable of forming resistive links on circuit boards is provided. Thisembodiment of the invention preferably does not contain any urethane Thesilver composition comprises an acrylated epoxy oligomer having, whereinthe acrylated epoxy oligomer is present in an amount of about 16% to 20%of the silver composition. The silver composition also comprises anisobornyl acrylate monomer in an amount of about 8% to 14% of the silvercomposition, an photoinitiator in an amount of about 4% to 8% of thesilver composition, a flow promoting agent in an amount of about 0.1% to2% of the silver composition, a silver powder in an amount of about 25%to 38% of the silver composition, and a silver flake composition in anamount of about 20% to 40% of the silver composition.

[0021] In accordance with yet another aspect of the invention, aphotocurable silver composition suitable for producing a coating that iscapable resistive links on circuit boards is provided. This embodimentcontains urethane. The silver composition comprises an aliphaticacrylated oligomer (a urethane), wherein the aliphatic acrylatedoligomer is present in an amount of about 7% to 11% of the silvercomposition. The silver composition further comprises an acrylated epoxyoligomer, wherein the acrylated epoxy oligomer is present in an amountof about 1% to 4% of the silver composition. The silver composition alsocomprises an isobornyl acrylate monomer in an amount of about 12% to 25%of the silver composition, a photoinitiator in an amount of about 2% to4% of the silver composition, a flow promoting agent in an amount ofabout 0.0% to 4% of the silver composition, an antimony tin oxide powderin an amount of 7% to 19%, a silver powder in an amount of about 24% to30% of the silver composition, and a silver flake composition in anamount of about 15% to 30% of the silver composition. In a furtherrefinement of this embodiment, the silver composition further comprisesa polyacrylic oligomer/acrylate monomer blend in an amount of about 5%to 10%.

[0022] In accordance with yet another aspect of the invention, aphotocurable silver composition suitable for producing a coating that iscapable black colored resistive links on circuit boards is provided. Thesilver composition comprises an aliphatic acrylated oligomer, whereinthe aliphatic acrylated oligomer is present in an amount of about 7% to11% of the silver composition The silver composition further comprisesan acrylated epoxy oligomer having, wherein the acrylated epoxy oligomeris present in an amount of about 2% to 4% of the silver composition. Thesilver composition also comprises an isobornyl acrylate monomer in anamount of about 10% to 14% of the silver composition, a photoinitiatorin an amount of about 13% to 15% of the silver composition, a flowpromoting agent in an amount of about 0.1% to 2% of the silvercomposition, a conductive carbon black powder in an amount of 5% to 12%,a wetting agent in an amount of about 0.5 to 3% of the silvercomposition, a silver powder in an amount of about 30% to 40% of thesilver composition, and a silver flake composition in an amount of about15% to 25% of the silver composition.

[0023] In accordance with another aspect of the invention, a method isprovided for making a photocurable silver composition. The methodcomprises a first step of combining and mixing an isobornyl acrylatemonomer and a photoinitiator to create a first mixture. The isobornylacrylate monomer is present in an amount of about 4% to 8% of the silvercomposition, and the photoinitiator is present in an amount of about 3%to 6% of the silver composition.

[0024] The method includes a second step of combining and mixing analiphatic acrylated oligomer and an acrylated epoxy oligomer to create asecond mixture. The aliphatic acrylated oligomer is present in an amountof about 3% to 8% of the silver composition and the acrylated epoxyoligomer is present in an amount of about 2% to 4% of the silvercomposition.

[0025] The method includes a third step of combining and mixing a silverpowder and a silver flake composition to create a third mixture. Thesilver powder is present in an amount of about 50% to 60% of the silvercomposition and the silver flake composition is present in an amount ofabout 25% to 35% of the silver composition.

[0026] The method further includes a fourth step of combining and mixinga flow promoting agent in an amount of about 0.1% to 2% of the silvercomposition, and a fifth step of combining the first, second, third andfourth mixtures to create the silver composition.

[0027] Preferably, but optionally, the first, second, third and fourthsteps are performed sequentially. The method in its various forms may becarried out on a batch basis, for example, in a mixing vessel or similarprocess equipment suitable for batch processing. It may also be carriedout in other forms, for example, such as continuous flow regimes.

[0028] In accordance with another aspect of the invention, anothermethod is provided for making a photocurable silver composition. Thismethod comprises a first step of combining and mixing an isobornylacrylate monomer and a photoinitiator to create a first composition,wherein the isobornyl acrylate monomer is present in an amount of about4% to 8% of the silver composition, and the photoinitiator is present inan amount of about 3% to 6% of the silver composition. This method alsoincludes a second step of combining with the first composition andmixing an aliphatic acrylated oligomer and an acrylated epoxy oligomerto create a second mixture. The aliphatic acrylated oligomer is presentin an amount of about 3% to 8% of the silver composition and theacrylated epoxy oligomer is present in an amount of about 2% to 4% ofthe silver composition.

[0029] The method further includes a third step of combining with thesecond composition and mixing a silver powder and a silver flakecomposition to create a third composition. The silver powder is presentin an amount of about 50% to 60% of the silver composition and thesilver flake composition is present in an amount of about 25% to 35% ofthe silver composition.

[0030] The method still further includes a fourth step of combining withthe third composition and mixing a flow promoting agent in an amount ofabout 0. 1% to 2% of the silver composition.

[0031] This method also may be carried out in a batch format, forexample, in a mixing vessel or series of mixing vessels, in a continuousflow regime, or in some combination.

[0032] In accordance with yet another aspect of the invention a methodis provided for depositing a silver coating on a substrate. The methodcomprises a first step of applying to the substrate a silver-containingfluid-phase composition (“silver composition”). The silver compositioncomprises an aliphatic acrylated oligomer, wherein the aliphaticacrylated oligomer is present in an amount of about 3% to 8% of thesilver composition. The silver composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 2% to 4% of the silver composition. The silver composition alsoincludes an isobornyl acrylate monomer in an amount of about 4% to 8% ofthe silver composition, a photoinitiator in an amount of about 3% to 6%of the silver composition, and a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition. The silver compositionfurther includes a silver powder in an amount of about 50% to 60% of thesilver composition, and a silver flake composition in an amount of about25% to 35% of the silver composition.

[0033] The method also includes a second step of illuminating the silvercomposition on the substrate with light of a wavelength suitable tocause the silver composition to cure into the silver coating. Preferablylight will have a wavelength in the ultraviolet region of theelectromagnetic spectrum.

[0034] In accordance with this method, the silver composition can beselectively deposited on the substrate at specific locations wheresilver plating is desired. It need not be applied to the entiresubstrate. It is thus possible, for example, to use the silver coatingthus created as metalizations on semiconductor wafers, printed circuitboards, pressure sensitive or pressure activated switches, and the like.

[0035] According to another aspect of the invention, a method isprovided for preparing a liquid-phase silver-containing composition foruse in providing a silver-containing coating or plating on a substrate.The presently preferred version of the method includes preparing thecomposition as identified immediately above. The method in broad termsincludes a first step of combining and mixing the monomer and thephotoinitiator in a mixing vessel, a second step of adding to the mixingvessel and blending in the urethane and the epoxy, a third step ofadding to the mixing vessel and blending in the silver powder and thesilver flake, and a forth step of adding to the mixing vessel andblending in the flow agent.

BEST MODE FOR CARRYING OUT THE INVENTION Silver Compositions

[0036] Reference will now be made in detail to presently preferredcompositions or embodiments and methods of the invention, whichconstitute the best modes of practicing the invention presently known tothe inventor.

[0037] In accordance with one aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. In this preferred embodiment, the silver composition includesan aliphatic acrylated oligomer. The aliphatic acrylated oligomer ispresent in an amount of about 3% to 8%, and preferably about 8%, of thesilver composition. The aliphatic acrylated oligomer preferablycomprises a urethane oligomer. Suitable aliphatic acrylated oligomersinclude Radcure Ebecryl 244, Ebecryl 264 and Ebecryl 284 urethanes,commercially available from Radcure UCB Corp. of Smyrna, Ga.; SartomerCN961, CN963, CN964, CN 966, CN982 and CN 983, commercially availablefrom Sartomer Corp. of Exton, Pa.; TAB FAIRAD 8010, 8179, 8205, 8210,8216, 8264, M-E-15, UVU-316, commercially available from TAB Chemicalsof Chicago, Ill.; and Echo Resin ALU-303, commercially available fromEcho Resins of Versaille, Mo.; and Genomer 4652, commercially availablefrom Rahn Radiation Curing of Aurora, Ill. The preferred aliphaticacrylated oligomers include Ebecryl 264 and Ebecryl 284. Ebecryl 264 isan aliphatic urethane triacrylate supplied as an 85% solution inhexandiol diacrylate. Ebecryl 284 is aliphatic urethane diacrylate of1200 molecular weight diluted with 1,6-hexandiol diacrylate. It isobvious to one skilled in the art that combinations of these materialsmay also be employed herein.

[0038] This preferred silver composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 2% to 4%, and preferably about 3%, of the silver composition.Suitable acrylated epoxy oligomers include Radcure Ebecryl 3603,commercially available from Radcure UCB Corp.; Sartomer CN120 and CN124,commercially available from Sartomer Corp.; and Echo Resin TME 9310 and9345, commercially available from Echo Resins. The preferred acrylatedepoxy oligomer is Ebecryl 3603, which tri-functional acrylated epoxynovolac. Combinations of these materials may also be employed herein.

[0039] The preferred silver composition also includes an isobornylacrylate monomer in an amount of about 4% to 8%, and preferably about5%, of the silver composition. Suitable isobornyl acrylate monomersinclude Sartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Preferred isobornyl acrylate monomers include SartomerSR423 IBOMA and SR506 IBOA; Radcure IBOA, commercially available fromRadcure Corp.; IBOA AND IBOMA, commercially available from CPS Chemical;and Genomer 1121, commercially available from Rahn Radiation Curing.

[0040] This preferred silver composition also includes a photoinitiatorin an amount of about 3% to 6%, and preferably about 4%, of the silvercomposition. Suitable photoinitiators include Irgacure 184(1-hydroxycyclohexyl phenyl ketone), 907(2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369(2-benzyl-2-N,N-dimethylamino- 1-(4-morpholinophenyl)- 1-butanone), 500(the combination of 1-hydroxy cyclohexyl phenyl ketone andbenzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (thecombination of bis(2,6-dimethoxybenzoyl-2,4-,4-trimethyl pentylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one),Ciba-Geigy 1700, and DAROCUR 1173 (2-hydroxy-2-methyl-1phenyl-1-propane)and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphineoxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), availablecommercially from Ciba-Geigy Corp., Tarrytown, N.Y.; CYRACURE UVI-6974(mixed triaryl sulfonium hexafluoroantimonate salts) and UVI-6990 (mixedtriaryl sulfonium hexafluorophosphate salts) available commercially fromUnion Carbide Chemicals and Plastics Co. Inc., Danbury, Conn.; andGenocure CQ, Genocure BOK, and GenocureMBF, commercially available fromRahn Radiation Curing. The preferred photoinitiator is Irgacure 1700commercially available from Ciba-Geigy of Tarrytown, N.Y.

[0041] The preferred silver composition still further includes a flowpromoting agent in an amount of about 0.1% to 2%, and preferably about1.0%, of the silver composition. Suitable flow promoting agents includeGenorad 17, commercially available from Rahn Radiation Curing; andModaflow, commercially available from Monsanto Chemical Co., St. Louis,Mo. The preferred flow promoting agent is Modaflow which is an ethylacrylate and 2-ethylhexyl acrylate copolymer that improves the flow ofthe composition. Combinations of these materials may also be employedherein.

[0042] The preferred silver composition also includes a silver powder inan amount of about 50% to 60%, and preferably about 52%, of the silvercomposition. The silver powder comprises a plurality of particles. Inthis preferred silver composition, the silver powder has a particle sizerange for these particles of about 5 microns to about 15 microns. Insome embodiments, the silver powder has a particle size range of about4.7 microns to about 14.9 microns. Preferably, the silver powderparticles have a particle size distribution wherein about 10% of theparticles have a particle size of less than about 4.7 microns, about 50%of the particles have a particle size of less than about 7.6 microns,and about 90% of the particles have a particle size of less than about14.9 microns. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

[0043] The preferred silver composition further includes a silver flakecomposition in an amount of about 25% to 35%, and preferably about 30%,of the silver composition. The silver flake composition comprises aplurality of flakes which comprise, and which preferably consistessentially of, silver. The silver flake composition according to thisembodiment has a particle size range of about 5 microns to about 32microns. More preferably, the silver flake composition has a particlesize range of about 5.5 microns to about 32.0 microns. The silver flakeparticle size distribution preferably is such that about 10% of theparticles have a particle size of less than about 5.5 microns, about 50%of the particles have a particle size of less than about 12.5 microns,and about 90% of the particles have a particle size of less than about32.0 microns. The preferred silver flake compositions are Silver Flake#25, Silver Flake #1, and Silver Flake #7A commercially available fromDegussa Corp. of South Plainfield, N.J.

EXAMPLE 1

[0044] This example provides a preferred silver composition according tothe invention that can be used for deposition on the surface of asubstrate such as a polymeric membrane, for example, to serve as theelectrical contact for a pressure-sensitive switch. The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 264 7.2 Ebecryl 3603 2.4 IBOA 4.7 SilverPowder EGED 53.4  Silver Flake # 25 27.6  Iragure 1700 3.9 Modaflow 0.8Total 100.00 

[0045] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. Finally, the mixing speed is increased to 10,000 rpm and mixedfor an additional 5 minutes.

[0046] For best results, the silver powder is washed prior to additionto the mixture. The washing process includes a first step of loading thepowder in a sealable container. A mixture consisting of 17% methyl ethylketone and 83% silver composition is added to the container and theslurry is mixed with a propeller blade for 5 minutes at 500 rpm. Themethyl ethyl ketone is poured off and the silver powder is allowed toair dry. During the drying stage the powder is periodically mixed.

[0047] The silver powder according to the presently-preferredcomposition comprises EGED, commercially available from Degussa Corp. ofSouth Plainfield, N.J. Such silver also may be obtained from othercommercial sources, e.g., such as Englehard Chemical Co. of Iselin, N.J.The presently preferred silver powder has a grain size distributionranging from about 5 microns to about 15 microns. This presentlypreferred silver powder has a particle size distribution as follows:TABLE 1 Silver Powder Particle Size Distribution Size Range (microns)Percentage <4.7 10% <7.6 50% <14.9  90%

[0048] As this table indicates, within a sample of the silver powder,10% of the grains have a size of less than 4.7 microns, 50% of thegrains have a particle size of less than 7.6 microns, and 90% of thegrains have a particle size of less than 14.9 microns.

[0049] The silver flake according to the presently-preferred compositionof Example I comprises SF25, commercially available from Degussa. Thissilver flake composition preferably has a grain size distributionranging from about 5 microns to about 32 microns. It has a particle sizedistribution as follows: TABLE 2 Silver Flake Composition Particle SizeDistribution Size Range (microns) Percentage  <5.5 10% <12.5 50% <32.090%

[0050] As indicated in Table 2, within a sample of the silver flake, 10%of the flakes have a size of less than 5.5 microns, 50% of the flakeshave a particle size of less than 12.5 microns, and 90% of the flakeshave a particle size of less than 32.0 microns.

EXAMPLE 2

[0051] This example provides another preferred silver compositionaccording to the invention that can be used for deposition on thesurface of a substrate such as those noted above. The silver compositionwas made from the following components: Component Approximate Mass %Ebecryl 264 4.2 Ebecryl 3603 2.7 IBOA 7.7 Silver Powder EGED 53.4 Silver Flake #25 27.6  Iragure 1700 3.8 Modaflow 0.6 Total 100.00 

[0052] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. Finally, the mixing speed is increased to 10,000 rpm and mixedfor an additional 5 minutes.

EXAMPLE 3

[0053] This example provides another preferred silver compositionaccording to the invention that can be used for deposition on thesurface of a substrate coated with indium tin oxide (ITO). The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 264 7.0 Ebecryl 3603 2.3 IBOA 4.6 SilverPowder EGED 52.3  Silver Flake # 25 27.0  Iragure 1700 3.8 Modaflow 0.8Ebecryl 168 2.2 Total 100.00 

[0054] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. In the next step, the Ebecryl 168 is added into the pan andthe combination mixed at 1000 rpm for 1 to 2 minutes. Finally, themixing speed is increased to 10,000 rpm and mixed for an additional 5minutes.

[0055] This example contains Ebecryl 168 added as an adhesion promoter.This material is a methacrylate ester derivative commercially availablefrom Radcure UCB Corp. of Smyrna, Georgia.

Silver Composition for Producing a Coating Capable Of ShieldingElectromagnetic Interference

[0056] In accordance with another aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a coating capableof shielding electromagnet interference. Such a coating may be appliedto substrates requiring shielding from electromagnetic interferencessuch as the interior of radio casings. In this preferred embodiment, thesilver composition includes an acrylated epoxy oligomer. The acrylatedepoxy oligomer is present in an amount of about 2% to 8%, and preferablyabout 5%, of the silver composition. Suitable acrylated epoxy oligomersare the same as listed above. The preferred acrylated epoxy oligomer isEbecryl 3603, which tri-functional acrylated epoxy novolac. Combinationsof these materials may also be employed herein.

[0057] The preferred silver composition also includes an isobornylacrylate monomer in an amount of about 15% to 30%, and preferably about21%, of the silver composition. Suitable isobornyl acrylate monomers arethe same as listed above. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

[0058] This preferred silver composition also includes a photoinitiatorin an amount of about 3% to 7%, and preferably about 5%, of the silvercomposition. Suitable photoinitiators are the same as listed above. Thepreferred photoinitiator is Irgacure 1700 commercially available fromCiba-Geigy of Tarrytown, N.Y. Combinations of these materials may alsobe employed herein.

[0059] The preferred silver composition still further includes a flowpromoting agent in an amount of about 0.1% to 2%, and preferably about1.0%, of the silver composition. Suitable flow promoting agents are thesame as listed above. The preferred flow promoting agent is Modaflowwhich is an ethyl acrylate and 2-ethylhexyl acrylate copolymer thatimproves the flow of the composition. Combinations of these materialsmay also be employed herein.

[0060] The preferred silver composition also includes a silver powder inan amount of about 25% to 40%, and preferably about 36%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

[0061] The preferred silver composition further includes a silver flakecomposition in an amount of about 20% to 40%, and preferably about 30%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 4

[0062] This example provides another preferred silver compositionaccording to the invention that when applied to a surface andsubsequently cured by ultraviolet radiation will produce a coatingsuitable for shielding electromagnetic interference. The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 3603 5.3 IBOA 21.0  Silver Powder EGED 31.5 Silver Flake # 1 35.7  Iragure 1700 5.3 Modaflow 1.2 Total 100.00 

[0063] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 3603, and the Modaflow are introduced into the pan andmixed for 5 minutes at a speed of 5000 rpm. In the next step, the EGEDsilver powder and the Silver Flake #1 are introduced into the pan andare mixed for 1 to 2 minutes at a speed of 1000 rpm. Finally, the mixingspeed is increased to 10,000 rpm and mixed for an additional 5 to 10minutes.

Non-Urethane Containing Silver Composition for Producing Resistive Links

[0064] In accordance with another aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a coating capableof producing resistive links in circuit boards. In this preferredembodiment, the silver composition includes an acrylated epoxy oligomer.The acrylated epoxy oligomer is present in an amount of about 16% to20%, and preferably about 18%, of the silver composition. Suitableacrylated epoxy oligomers are the same as listed above. The preferredacrylated epoxy oligomer is Ebecryl 3603, which tri-functional acrylatedepoxy novolac. Combinations of these materials may also be employedherein.

[0065] The preferred silver composition also includes an isobornylacrylate monomer in an amount of about 8% to 14%, and preferably about11%, of the silver composition. Suitable isobornyl acrylate monomers arethe same as listed above. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA AND IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

[0066] This preferred silver composition also includes a photoinitiatorin an amount of about 4% to 8%, and preferably about 6%, of the silvercomposition. Suitable photoinitiators are the same as those listedabove. The preferred photoinitiator is Irgacure 1700 commerciallyavailable from Ciba-Geigy of Tarrytown, N.Y. Combinations of thesematerials may also be employed herein.

[0067] The preferred silver composition still further includes a flowpromoting agent in an amount of about 0.1% to 2%, and preferably about1.0%, of the silver composition. Suitable flow promoting agents are thesame as those listed above. The preferred flow promoting agent isModaflow which is an ethyl acrylate and 2-ethylhexyl acrylate copolymerthat improves the flow of the composition. Combinations of thesematerials may also be employed herein.

[0068] The preferred silver composition also includes a silver powder inan amount of about 25% to 35%, and preferably about 30%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

[0069] The preferred silver composition further includes a silver flakecomposition in an amount of about 25% to 38%, and preferably about 34%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

[0070] To illustrate, the following example sets forth a presentlypreferred silver composition according to this aspect of the invention.

EXAMPLE 5

[0071] This example provides another preferred silver compositionaccording to the invention that when applied to a surface andsubsequently cured by ultraviolet radiation will produce a coatingsuitable for making resistive links on circuit board. The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 3603 18.3 IBOA 11.1 Silver Powder EGED 30.0Silver Flake #1 33.5 Irgacure 1700  6.1 Modaflow  1.0 Total 100.00

[0072] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 3603 and the Modaflow are introduced into the pan andmixed for 5 minutes at a speed of 5000 rpm. In the next step, the EGEDsilver powder and the Silver Flake #1 are introduced into the pan andare mixed for 1 to 2 minutes at a speed of 1000 rpm. Finally, the mixingspeed is increased to 10,000 rpm and mixed for an additional 5 to 10minutes.

Urethane Containing Silver Composition for Producing Resistive Links

[0073] In accordance with one aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a coating capableof producing resistive links in circuit boards. In this preferredembodiment, the silver composition includes an aliphatic acrylatedoligomer. The aliphatic acrylated oligomer is present in an amount ofabout 7% to 11%, and preferably about 9%, of the silver composition. Thealiphatic acrylated oligomer preferably comprises a urethane oligomer.Suitable aliphatic acrylated oligomers are the same as those listedabove. The preferred aliphatic acrylated oligomers include Ebecryl 264and Ebecryl 284. Ebecryl 264 is an aliphatic urethane triacrylatesupplied as an 85% solution in hexandiol diacrylate. Ebecryl 284 isaliphatic urethane diacrylate of 1200 molecular weight diluted with1,6-hexandiol diacrylate. Combinations of these materials may also beemployed herein.

[0074] This preferred silver composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 1% to 4%, and preferably about 3%, of the silver composition.Suitable acrylated epoxy oligomers are the same as those listed above.The preferred acrylated epoxy oligomer is Ebecryl 3603, whichtri-functional acrylated epoxy novolac. Combinations of these materialsmay also be employed herein.

[0075] The preferred silver composition also includes an isobornylacrylate monomer in an amount of about 12% to 25%, and preferably about22%, of the silver composition. Preferred isobornyl acrylate monomersinclude Sartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

[0076] This preferred silver composition also includes a photoinitiatorin an amount of about 2% to 4%, and preferably about 3%, of the silvercomposition. Suitable photoinitiators are the same as those listedabove. The preferred photoinitiator is Irgacure 1700 commerciallyavailable from Ciba-Geigy of Tarrytown, N.Y.

[0077] The preferred silver composition further includes a antimony tinoxide powder in an amount of 7% to 19%, and preferable about 17% of thesilver composition. The preferred antimony tin oxide powder in Minatec40 commercially available from EM Industries of Hawthorne, N.Y.

[0078] The preferred silver composition still further includes a flowpromoting agent in an amount of about 0.0% to 4%, and preferably about2.0%, of the silver composition. Suitable flow promoting agents are thesame as those listed above. The preferred flow promoting agent isModaflow which is an ethyl acrylate and 2-ethylhexyl acrylate copolymerthat improves the flow of the composition.

[0079] The preferred silver composition also includes a silver powder inan amount of about 24% to 30%, and preferably about 27%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

[0080] The preferred silver composition further includes a silver flakecomposition in an amount of about 15% to 30%, and preferably about 17%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 6

[0081] This example provides another preferred silver compositionaccording to the invention that when applied to a surface andsubsequently cured by ultraviolet radiation will produce a coatingsuitable for making resistive links on circuit board. The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 264  8.7 Ebecryl 3603  2.9 IBOA 22.4 SilverFlake # 7A 17.0 Silver powder CED 26.5 Minatec 40 17.2 Iragure 1700  3.3Modaflow  2.0 Total 100.00

[0082] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the CED silver powder, the Minatec 40, and the Silver Flake#7A are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the mixing speed is increased to 10,000 rpmand mixed for an additional 5 minutes.

EXAMPLE 7

[0083] This example provides another preferred silver compositionaccording to the invention that when applied to a surface andsubsequently cured by ultraviolet radiation will produce a coatingsuitable for making resistive links on circuit board. The silvercomposition was made from the following components: ComponentApproximate Mass % Ebecryl 284 8.4 Ebecryl 3603 1.7 Ebecryl 754 8.4 IBOA15.7  Silver Powder CED 25.0  Silver Flake # 7A 28.5  Iragure 1700 2.5Minatec 40 9.8 Total 100.00 

[0084] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 754, Ebecryl 284, the Ebecryl 3603, and the Modafloware introduced into the pan and mixed for 1 to 2 minutes at a speed of1000 rpm. In the next step, the CED silver powder, and the Silver Flake#7A are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the mixing speed is increased to 10,000 rpmand mixed for an additional 5 minutes.

[0085] This example contains Ebecryl 754 as an additive. Ebecryl 754 isa polyacrylic oligomer/acrylate monomer blend commercially availablefrom Radcure UCB Corp. of Smyrna, Ga.

Black Colored Silver Composition for Producing Resistive Links

[0086] In accordance with one aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a dark-coloredcoating capable of producing resistive links in circuit boards. In thispreferred embodiment, the silver composition includes an aliphaticacrylated oligomer. The aliphatic acrylated oligomer is present in anamount of about 7% to 11%, and preferably about 9%, of the silvercomposition. The aliphatic acrylated oligomer preferably comprises aurethane oligomer. Suitable aliphatic acrylated oligomers are the sameas those listed above. The preferred aliphatic acrylated oligomersinclude Ebecryl 264 and Ebecryl 284. Ebecryl 264 is an aliphaticurethane triacrylate supplied as an 85% solution in hexandioldiacrylate. Ebecryl 284 is aliphatic urethane diacrylate of 1200molecular weight diluted with 1,6-hexandiol diacrylate. Combinations ofthese materials may also be employed herein.

[0087] This preferred silver composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 2% to 4%, and preferably about 3%, of the silver composition.Suitable acrylated epoxy oligomers are the same as those listed above.The preferred acrylated epoxy oligomer is Ebecryl 3603, whichtri-functional acrylated epoxy novolac.

[0088] The preferred silver composition also includes an isobornylacrylate monomer in an amount of about 10% to 14%, and preferably about12%, of the silver composition. Preferred isobornyl acrylate monomersinclude Sartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA AND IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing.

[0089] This preferred silver composition also includes a photoinitiatorin an amount of about 13% to 15%, and preferably about 14%, of thesilver composition. The preferred photoinitiator is Irgacure 1700commercially available from Ciba-Geigy of Tarrytown, N.Y.

[0090] The preferred silver composition further includes a carbon blackpowder in an amount of 5% to 12%, and preferable about 7% of the silvercomposition. The preferred carbon black powder is Printex L commerciallyavailable from EM Industries of Hawthorne, N.Y.

[0091] The preferred silver composition further includes a wetting agentin an amount of 0.5% to 3%, and preferable about 1.5% of the silvercomposition. The preferred wetting agent is BYK 207 L commerciallyavailable from Byk-Chemie of Wallingford, Conn.

[0092] The preferred silver composition still further includes a flowpromoting agent in an amount of about 0.1% to 2%, and preferably about1.0%, of the silver composition. The preferred flow promoting agent isModaflow which is an ethyl acrylate and 2-ethylhexyl acrylate copolymerthat improves the flow of the composition. It is obvious to one skilledin the art that combinations of these materials may also be employedherein.

[0093] The preferred silver composition also includes a silver powder inan amount of about 30% to 40%, and preferably about 36%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

[0094] The preferred silver composition further includes a silver flakecomposition in an amount of about 15% to 25%, and preferably about 18%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 8

[0095] This example provides another preferred silver compositionaccording to the invention that when applied to a surface andsubsequently cured by ultraviolet radiation will produce a coatingsuitable for making black colored resistive links on circuit board. Thesilver composition was made from the following components: ComponentApproximate Mass % Ebecryl 264 8.8 Ebecryl 3603 2.5 Printex L 7.3 Byk207 1.5 IBOA 11.6  Silver Powder EGED 35.7  Silver Flake # 25 18.4 Iragure 1700 13.5  Modaflow 0.7 Total 100.00 

[0096] In this example the IBOA and Iragure 1700 are mixed in a pan witha propeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, the Silver Flake #25, and the PrintexL are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the BYK 207 in introduced and mixed for 5minutes at a speed of 10,000 rpm.

[0097] In describing each of the components in these examples and inthis description, the compositions have been described as “comprising”the stated component. Preferably each of those components consistsessentially of, and more preferably they consist exclusively of, thestated components, and from the stated sources.

[0098] The silver-containing composition as described above is referredto as being a “fluid phase” composition. This is meant to indicate thatthe composition is flowable as is a liquid, but is not otherwiselimiting. Preferably, the silver composition comprises a liquid. Thecomposition, for example, generally will be a slurry, in which thesilver metal grains (powder and flakes) are solid-phase particlessuspended in the liquid phase or phases of the urethane, epoxy, and anyother liquid or essentially liquid components.

Method for Preparing Silver Composition

[0099] In accordance with another aspect of the invention, a method isprovided for making a photocurable silver composition. In accordancewith a preferred version, the method includes a first step of combiningand mixing an isobornyl acrylate monomer and a photoinitiators to createa first mixture. The isobornyl acrylate monomer is present in an amountof about 4% to 8% of the silver composition, and the photoinitiator ispresent in an amount of about 4% to 6% of the silver composition.

[0100] This preferred method preferably but optionally is carried outusing a mixing vessel of appropriate size, depending upon the desiredbatch size. A glass or steel lined batch processing vessel of knowndesign and commercial availability typically will suffice.

[0101] This first step of the preferred method is carried out by placingthe components into the vessel while stirring, e.g., by a suitableimpeller.

[0102] The method includes a second step of combining and mixing analiphatic acrylated oligomer and an acrylated epoxy oligomer to create asecond mixture. The aliphatic acrylated oligomer is present in an amountof about 3% to 8% of the silver composition and the acrylated epoxyoligomer is present in an amount of about 2% to 4% of the silvercomposition. In accordance with this preferred method, this second stepis carried out sequentially after the first step, and involves blendingin these components into the first mixture, i.e., from the first step.

[0103] The method further includes a third step of combining and mixinga silver powder and a silver flake composition to create a thirdmixture. The silver powder is present in an amount of about 50% to 60%of the silver composition and the silver flake composition is present Anamount of about 25% to 35% of the silver composition. This step alsopreferably is carried out in the vessel, preferably sequentially aftercompletion of the second step.

[0104] The method further includes a fourth step of combining and mixinga flow promoting agent in an amount of about 0.1% to 2% of the silvercomposition, and a fifth step of combining the first, second, third andfourth mixtures to create the silver composition.

[0105] These steps also preferably would be performed sequentially byadding the cited components into the vessel while mixing with theimpeller.

[0106] As noted, preferably but optionally, the first, second, third andfourth steps are performed sequentially. This is not, however, limiting.Different processing orders may be used in accordance with the method.

[0107] Also as noted, the method in its various forms may be carried outon a batch basis, for example, in a mixing vessel or similar processequipment suitable for batch processing. It may also be carried out inother forms, for example, such as continuous flow regimes, e.g., usingknown continuous flow processing equipment and configurations for mixingthese components, preferably but optionally in the sequential orderidentified above.

[0108] In accordance with another aspect of the invention, anothermethod is provided for making an ultraviolet curable silver composition.This method comprises a first step of combining and mixing an isobornylacrylate monomer and a photoinitiator to create a first composition,wherein the isobornyl acrylate monomer is present in an amount of about4% to 8% of the silver composition, and the photoinitiator is present inan amount of about 3% to 6% of the silver composition. This method alsoincludes a second step of combining with the first composition andmixing an aliphatic acrylated oligomer and an acrylated epoxy oligomerto create a second mixture. The aliphatic acrylated oligomer is presentin an amount of about 3% to 8% of the silver composition and theacrylated epoxy oligomer is present in an amount of about 2% to 4% ofthe silver composition.

[0109] The method further includes a third step of combining with thesecond composition and mixing a silver powder and a silver flakecomposition to create a third composition. The silver powder is presentin an amount of about 50% to 60% of the silver composition and thesilver flake composition is present in an amount of about 25% to 35% ofthe silver composition.

[0110] The method still further includes a fourth step of combining withthe third composition and mixing a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition.

[0111] According to another aspect of the invention, a method isprovided for preparing a liquid-phase silver-containing composition foruse in providing a silver-containing coating, plating, film or layer ona substrate. The presently-preferred version of the method includespreparing either of the preferred silver compositions as identified inthe examples above. The preferred version of this method includes afirst step of combining and mixing the monomer and the photoinitiator ina mixing vessel. The method includes a second step of adding to themixing vessel and blending into the previously-added components theurethane and the epoxy. The method also includes a third step of addingto the mixing vessel and blending into the components therein the silverpowder and the silver flake. The preferred method further includes afourth step of adding to the mixing vessel and blending into itspreviously-added components the flow agent.

Method for Depositing a Silver Coating on a Substrate

[0112] In accordance with still another aspect of the invention, amethod is provided for depositing a silver coating on a substrate. Themethod comprises a first step of applying a silver-containingfluid-phase composition (“silver composition”) to the substrate. Each ofthe silver compositions described above are suitable for application tothe substrate.

[0113] In a preferred embodiment, the silver composition that is appliedto the substrate comprises an aliphatic acrylated oligomer, thealiphatic acrylated oligomer being present in an amount of about 3% to8% of the silver composition; an acrylated epoxy oligomer, the acrylatedepoxy oligomer being present in an amount of about 2% to 4% of thesilver composition; an isobornyl acrylate monomer in an amount of about4% to 8% of the silver composition; a photoinitiator in an amount ofabout 3% to 6% of the silver composition; a flow promoting agent in anamount of about 0.1% to 2% of the silver composition; a silver powder inan amount of about 50% to 60% of the silver composition; and a silverflake composition in an amount of about 25% to 35% of the silvercomposition. The preferred silver compositions according to this methodare those described herein, for example, including the compositionsdescribed in the examples.

[0114] The silver composition may be applied to the substrate using anumber of different techniques. The silver composition may be applied,for example, by direct brush application, or it may be sprayed onto thesubstrate surface. It also may be applied using a screen printingtechnique. In such screen printing technique, a “screen” as the term isused in the screen printing industry is used to regulate the flow ofliquid composition onto the substrate surface. The silver compositiontypically would be applied to the screen as the latter contacts thesubstrate. The silver composition flows through the silk screen to thesubstrate, whereupon it adheres to the substrate An the desired filmthickness. Screen printing techniques suitable for this purpose includeknown techniques, but wherein the process is adjusted in ways known topersons of ordinary skill in the art to accommodate the viscosity,flowability, and other properties of the liquid-phase composition, thesubstrate and its surface properties, etc. Flexographic techniques, forexample, using pinch rollers to contact the silver composition with arolling substrate, also may be used.

[0115] The method includes a second step of illuminating thesilver-containing fluid-phase composition on the substrate with anultraviolet light to cause the silver-containing fluid-phase compositionto cure into the silver coating. This illumination may be carried out inany number of ways, provided the ultraviolet light or radiation impingesupon the silver composition so that the silver composition is caused topolymerize to form the coating, layer, film, etc., and thereby cures.Such formed layers have a resistivity from 0.03 to 0.50 ohms/sq at 1mil.

[0116] Curing preferably takes place by free radical polymerization,which is initiated by an ultraviolet radiation source. Thephotoinitiator preferably comprises a photoinitiator, as describedabove.

[0117] Various ultraviolet light sources may be used, depending on theapplication. Preferred ultraviolet radiation sources for a number ofapplications include known ultraviolet lighting equipment with energyintensity settings of, for example, 125 watts, 200 watts, and 300 wattsper square inch.

[0118] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, representative devices,and illustrative examples shown and described. Accordingly, departuresmay be made from such details without departing from the spirit or scopeof the general inventive concept.

What is claimed is:
 1. A photocurable silver composition consistingessentially of: a photocurable organic mixture; a photoinitiator; silverpowder; and silver flakes in an amount of at least 20% relative to theweight of the silver powder, the photocurable silver composition whenilluminated with ultraviolet (UV) light cures into a silver coating. 2.The photocurable silver composition of claim 1 wherein the photocurableorganic mixture comprises an aliphatic acrylated urethane oligomer. 3.The silver composition recited in claim 2 , wherein the aliphaticacrylated urethane oligomer is present in an amount of about 3% to 8% ofthe silver composition.
 4. The silver composition recited in claim 2 ,wherein the aliphatic acrylated urethane oligomer is present in anamount of about 8% of the silver composition.
 5. The photocurable silvercomposition of claim 2 wherein the photocurable organic mixture furthercomprises an acrylated epoxy oligomer.
 6. The silver composition recitedin claim 5 , wherein the acrylated epoxy oligomer is present in anamount of about 2% to 4% of the silver composition.
 7. The silvercomposition recited in claim 5 , wherein the acrylated epoxy oligomer ispresent in an amount of about 3% of the silver composition.
 8. Thephotocurable silver composition of claim 5 wherein the photocurableorganic mixture further comprises an isobornyl acrylate monomer.
 9. Thesilver composition recited in claim 8 , wherein the isobornyl acrylatemonomer is present in an amount of about 4% to 8% of the silvercomposition.
 10. The silver composition recited in claim 8 , wherein theisobornyl acrylate monomer is present in an amount of about 5% of thesilver composition.
 11. The silver composition recited in claim 8 ,wherein the photocurable organic mixture further comprises a flowpromoting agent.
 12. The silver composition recited in claim 11 ,wherein the flow agent is present in an amount of about 0.1% to 2% ofthe silver composition.
 13. The silver composition recited in claim 11 ,wherein the flow agent is present in an amount of about 1% of the silvercomposition.
 14. The silver composition recited in claim 1 , wherein thesilver powder is present in an amount of about 50% to 60% of the silvercomposition.
 15. A silver composition as recited in claim 1 , whereinthe silver powder is present in an amount of about 52% of the silvercomposition.
 16. The silver composition recited in claim 1 , wherein thesilver flakes are present in an amount of about 25% to 35% of the silvercomposition.
 17. The silver composition recited in claim 1 , wherein thesilver flakes is present in an amount of about 5% of the silvercomposition.
 18. The silver composition recited in claim 1 , wherein thephotoinitiator is present in an amount of about 3% to 6% of the silvercomposition.
 19. The silver composition recited in claim 1 , wherein thephotoinitiator is present in an amount of about 5% of the silvercomposition.
 20. A method for depositing a silver coating on asubstrate, the method comprising: a first step of applying to thesubstrate a composition comprising: an aliphatic acrylated urethaneoligomer; an acrylated epoxy oligomer; an isobornyl acrylate monomer; aphotoinitiator; silver powder; and silver flakes in an amount of atleast 20% relative to the weight of the silver powder; and a second stepof photocuring by exposure to light of a wavelength effective to curesaid composition.
 21. A method as recited in claim 20 , wherein thefirst step comprises spraying the silver-containing fluid-phasecomposition onto the substrate.
 22. A method as recited in claim 20 ,wherein the first step comprises applying the silver-containingfluid-phase composition to the substrate using a screen printingtechnique.
 23. A method as recited in claim 20 , wherein the first stepcomprises applying the silver-containing fluid-phase composition to thesubstrate using a flexographic technique.